1. Field of the Invention
The present invention relates to a video signal conversion apparatus and, more particularly, to an apparatus for interpolating a color-difference line-sequential video signal.
2. Description of the Prior Art
A color-difference line-sequential color video signal system is used with an electronic still camera, a color-difference line-sequential color television (TV) system, and others. As well known in the art, a color-difference line-sequential color video signal system is such that two different kinds of color-difference signals appear alternately on a horizontal scanning line basis. For example, in a certain system, one of two color-difference signals R-Y and B-Y appears on one scanning line, and the other on the next scanning line successively.
Some modern solid-state imaging devices are provided with a delay circuit for delaying a color-difference signal by one horizontal scanning (1H) period before producing it, so that one missing color-difference signal is produced. Usually, such a delay circuit is constructed to delay a color-difference signal by 1H period without applying analog-to-digital conversion to the signal, the delayed signal thus composes the one missing color-difference signal. Hence, the same line of the color-difference signal appears continuously over 2H period.
Generally a color-difference signal which is delayed by an analog delay circuit as stated above is not of good quality since it contains abundance of noise. Insofar as an ordinary video monitor, using two-field, one-frame interlace scanning system is used to reproduce a video signal which contains such delayed signal components, the picture may not appear so degraded. However, when it comes to a hard copy which is produced by recording the picture, as represented by the video signal, on a recording medium, the degradation in the quality of the picture due to the deterioration of the signal is conspicuous. Such a degradation is more pronounced in still pictures than in moving pictures and in hard copies than in soft copies.